An inkjet printer well known in the art prints images by ejecting ink droplets through nozzles to form dots on recording paper. However, manufacturing error may cause the impact positions of ink droplets ejected from this inkjet printer to deviate from intended positions, producing white streaks in the image called “banding” that reduces the overall image quality. Banding is a white area of the recording paper that appears as a white line when the gap between adjacent dots grows too large.
Two types of inkjet printers are a multi-pass printer and a line head printer. The multi-pass printer prints images on recording paper by ejecting ink droplets through nozzles formed in the ink head while reciprocating the ink head in a main scanning direction orthogonal to the paper-conveying direction. The line head printer, on the other hand, has a very long print head, equivalent to or greater than the width of the recording paper and having rows of nozzles capable of forming dots in full line units so that the printer can print images without reciprocating the ink head.
The multi-pass printer can suppress the above-mentioned problem of banding to a degree by adjusting the distance between dots in the main scanning direction orthogonal to the paper-conveying direction based on the position of the ink head in the main scanning direction. However, since the ink head is not reciprocated in a line head printer, the distance between dots in the direction orthogonal to the paper-conveying direction is fixed based on the positions of the nozzles and is very difficult to adjust. Hence, the line head printer is susceptible to banding caused by a gap between dots at the same position relative to the longitudinal direction of the print head when the gaps are linked in a series extending in the paper-conveying direction.
One conventional image-forming device has a long ink head constructed by linking a plurality of heads in the longitudinal direction so that the ends of adjacent heads overlap. This conventional image-forming device suppresses banding by adjusting the size of ink dots ejected from nozzles in areas that the ink heads overlap. Another conventional image-forming device prevents a decline in the width of an image caused by inclination in the print head by adding an extra pixel or modifying the size of the dots.